Broadcasting and telecommunications have historically occupied separate fields. In the past, broadcasting was largely an “over-the-air” medium while wired media carried telecommunications. That distinction may no longer apply as both broadcasting and telecommunications may be delivered over either wired or wireless media. Present development may adapt broadcasting to mobility services. One limitation has been that broadcasting may often require high bit rate data transmission at rates higher than could be supported by existing mobile communications networks. However, with emerging developments in wireless communications technology, even this obstacle may be overcome.
Terrestrial television and radio broadcast networks have made use of high power transmitters covering broad service areas, which enable one-way distribution of content to user equipment such as televisions and radios. By contrast, wireless telecommunications networks have made use of low power transmitters, which have covered relatively small areas known as “cells”. Unlike broadcast networks, wireless networks may be adapted to provide two-way interactive services between users of user equipment such as telephones and computer equipment.
The introduction of cellular communications systems in the late 1970's and early 1980's represented a significant advance in mobile communications. The networks of this period may be commonly known as first generation, or “1G” systems. These systems were based upon analog, circuit-switching technology, the most prominent of these systems may have been the advanced mobile phone system (AMPS). Second generation, or “2G” systems ushered improvements in performance over 1G systems and introduced digital technology to mobile communications. Exemplary 2G systems include the global system for mobile communications (GSM), digital AMPS (D-AMPS), and code division multiple access (CDMA). Many of these systems have been designed according to the paradigm of the traditional telephony architecture, often focused on circuit-switched services, voice traffic, and supported data transfer rates up to 14.4 kbits/s. Higher data rates were achieved through the deployment of “2.5G” networks, many of which were adapted to existing 2G network infrastructures. The 2.5G networks began the introduction of packet-switching technology in wireless networks. However, it is the evolution of third generation, or “3G” technology that may introduce fully packet-switched networks, which support high-speed data communications.
The general packet radio service (GPRS), which is an example of a 2.5G network service oriented for data communications, comprises enhancements to GSM that required additional hardware and software elements in existing GSM network infrastructures. Where GSM may allot a single time slot in a time division multiple access (TDMA) frame, GPRS may allot up to 8 such time slots providing a data transfer rate of up to 115.2 kbits/s. Another 2.5G network, enhanced data rates for GSM evolution (EDGE), also comprises enhancements to GSM, and like GPRS, EDGE may allocate up to 8 time slots in a TDMA frame for packet-switched, or packet mode, transfers. However, unlike GPRS, EDGE adapts 8 phase shift keying (8-PSK) modulation to achieve data transfer rates that may be as high as 384 kbits/s.
The universal mobile telecommunications system (UMTS) is an adaptation of a 3G system, which is designed to offer integrated voice, multimedia, and Internet access services to portable user equipment. The UMTS adapts wideband CDMA (W-CDMA) to support data transfer rates, which may be as high as 2 Mbits/s. One reason why W-CDMA may support higher data rates is that W-CDMA channels may have a bandwidth of 5 MHz versus the 200 kHz channel bandwidth in GSM. A related 3G technology, high speed downlink packet access (HSDPA), is an Internet protocol (IP) based service oriented for data communications, which adapts W-CDMA to support data transfer rates of the order of 10 Mbits/s. HSDPA achieves higher data rates through a plurality of methods. For example, many transmission decisions may be made at the base station level, which is much closer to the user equipment as opposed to being made at a mobile switching center or office. These may include decisions about the scheduling of data to be transmitted, when data are to be retransmitted, and assessments about the quality of the transmission channel. HSDPA may also utilize variable coding rates in transmitted data. HSDPA also supports 16-level quadrature amplitude modulation (16-QAM) over a high-speed downlink shared channel (HS-DSCH), which permits a plurality of users to share an air interface channel.
The multiple broadcast/multicast service (MBMS) is an IP datacast service, which may be deployed in EDGE and UMTS networks. The impact of MBMS is largely within the network in which a network element adapted to MBMS, the broadcast multicast service center (BM-SC), interacts with other network elements within a GSM or UMTS system to manage the distribution of content among cells within a network. User equipment may be required to support functions for the activation and deactivation of MBMS bearer service. MBMS may be adapted for delivery of video and audio information over wireless networks to user equipment. MBMS may be integrated with other services offered over the wireless network to realize multimedia services, such as multicasting, which may require two-way interaction with user equipment.
Standards for digital television terrestrial broadcasting (DTTB) have evolved around the world with different systems being adopted in different regions. The three leading DTTB systems are, the advanced standards technical committee (ATSC) system, the digital video broadcast terrestrial (DVB-T) system, and the integrated service digital broadcasting terrestrial (ISDB-T) system. The ATSC system has largely been adopted in North America, South America, Taiwan, and South Korea. This system utilizes trellis coding and 8-level vestigial sideband (8-VSB) modulation techniques. The DVB-T system has largely been adopted in Europe, the Middle East, Australia, as well as parts of Africa and parts of Asia. The DVB-T system adapts coded orthogonal frequency division multiplexing (COFDM). The ISDB-T system has been adopted in Japan and adapts bandwidth segmented transmission orthogonal frequency division multiplexing (BST-OFDM).
The various DTTB systems may differ in important aspects; some systems employ a 6 MHz channel separation, while others may employ 7 MHz or 8 MHz channel separations. Planning for the allocation of frequency spectrum may also vary among countries with some countries integrating frequency allocation for DTTB services into the existing allocation plan for legacy analog broadcasting systems. In such instances, broadcast towers for DTTB may be co-located with broadcast towers for analog broadcasting services with both services being allocated similar geographic broadcast coverage areas. In other countries, frequency allocation planning may involve the deployment of single frequency networks (SFNs), in which a plurality of towers, possibly with overlapping geographic broadcast coverage areas (also known as “gap fillers”), may simultaneously broadcast identical digital signals. SFNs may provide very efficient use of broadcast spectrum as a single frequency may be used to broadcast over a large coverage area in contrast to some of the conventional systems, which may be used for analog broadcasting, in which gap fillers transmit at different frequencies to avoid interference.
Even among countries adopting a common DTTB system, variations may exist in parameters adapted in a specific national implementation. For example, DVB-T not only supports a plurality of modulation schemes, comprising quadrature phase shift keying (QPSK), 16-QAM, and 64 level QAM (64-QAM), but DVB-T offers a plurality of choices for the number of modulation carriers to be used in the COFDM scheme. The “2K” mode permits 1,705 carrier frequencies that may carry symbols, each with a useful duration of 224 μs for an 8 MHz channel. In the “8K” mode there are 6,817 carrier frequencies, each with useful symbol duration of 896 μs for an 8 MHz channel. In SFN implementations, the 2K mode may provide comparatively higher data rates but smaller geographical coverage areas than may be the case with the 8K mode. Different countries adopting the same system may also employ different channel separation schemes.
While 3G systems are evolving to provide integrated voice, multimedia, and data services to mobile user equipment, there may be compelling reasons for adapting DTTB systems for this purpose. One of the more notable reasons may be the high data rates that may be supported in DTTB systems. For example, DVB-T may support data rates of 15 Mbits/s in an 8 MHz channel in a wide area SFN. There are also significant challenges in deploying broadcast services to mobile user equipment. Many handheld portable devices, for example, may require that services consume minimum power to extend battery life to a level, which may be acceptable to users. Another consideration is the Doppler effect in moving user equipment, which may cause inter-symbol interference in received signals. Among the three major DTTB systems, ISDB-T was originally designed to support broadcast services to mobile user equipment. While DVB-T may not have been originally designed to support mobility broadcast services, a number of adaptations have been made to provide support for mobile broadcast capability. The adaptation of DVB-T to mobile broadcasting is commonly known as DVB handheld (DVB-H).
To meet requirements for mobile broadcasting the DVB-H specification may support time slicing to reduce power consumption at the user equipment, addition of a 4K mode to enable network operators to make tradeoffs between the advantages of the 2K mode and those of the 8K mode, and an additional level of forward error correction on multiprotocol encapsulated data—forward error correction (MPE-FEC) to make DVB-H transmissions more robust to the challenges presented by mobile reception of signals and to potential limitations in antenna designs for handheld user equipment. DVB-H may also use the DVB-T modulation schemes, like QPSK and 16-quadrature amplitude modulation (16-QAM), which may be most resilient to transmission errors. MPEG audio and video services may be more resilient to error than data, thus additional forward error correction may not be required to meet DTTB service objectives.
In a conventional wireless communication system, one or more handheld devices may receive information via a downlink communication path. However, channel conditions of the downlink communication path may vary, which may result in poor quality of the received information at the receiver. Furthermore, any information, which was not received by the receiver, may be re-transmitted which may result in processing delay.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.